To anyone that's remotely interested, I'd really suggest getting yourself a copy of PICO-8 to fiddle with. When people post their games, they include all the code/assets by default, so there's a ton of stuff to read and learn from and it generally is a fun tool to mess with. I'm working on my first Tetris clone atm myself
Indeed, the PICO-8 BBS [1] is a smorgasbord of open-source games of various kinds and quality.
A lot of people (including me) practice extreme open-source for PICO-8 carts by licensing them as Creative Commons, which is easy to do - you just click a checkbox on submission.
This in turn leads to the best games being tweaked and remixed quite a lot - for example Celeste [2] (in my opinion, the best game on the platform) has at least one variant with a lot of new mechanics and gameplay [3].
